Finish revs.1.23 and 1.24 so that MCOUNT_ENTER really actually compiles

for SMP in the plain profiling case.  It seems to work too.

This error was not detected by LINT because LINT only compiles the
GUPROF profiling case, which is is a superset of the plain profiling
case for !SMP but which is so broken for SMP that the buggy code is
not compiled.

sys/amd64/include/profile.h

@@ -64,6 +64,7 @@
 #else
 #define	MCOUNT_DECL(s)	u_long s;
 #ifdef SMP
+extern int	mcount_lock;
 #define	MCOUNT_ENTER(s)	{ s = read_eflags(); disable_intr(); \
  			  while (!atomic_cmpset_acq_int(&mcount_lock, 0, 1)) \
 			  	/* nothing */ ; }

sys/i386/include/profile.h

@@ -64,6 +64,7 @@
 #else
 #define	MCOUNT_DECL(s)	u_long s;
 #ifdef SMP
+extern int	mcount_lock;
 #define	MCOUNT_ENTER(s)	{ s = read_eflags(); disable_intr(); \
  			  while (!atomic_cmpset_acq_int(&mcount_lock, 0, 1)) \
 			  	/* nothing */ ; }